Such a mixing valve is known from German 38 20 855. In this mixing valve a relatively large-diameter dome-shaped and squat knob serves for controlling both the valves. To select hot water or cold water the user turns this knob in the appropriate direction, which can lead to mistakes. In addition the gears of the valve are not always in mesh with the teeth of the knob, so that they clash as the come together and rotation of the knob is often blocked.